Blending 2 clips side by side

[Vincent Rosati]

That looks more like a job for After Effects – using layer masks and feathering.
It looks like you want to feather three clips together, side by side.

You could create Alpha Mattes (in PhotoShop)to composite and feather the edges, for use with the Track Matte Key effect in Premiere.
You might have the center portion at full opacity, than create two alpha channel images to control the blending/feathering of the video that will run on the left and right sides.
The left side alpha would be solid white (pass-through) on the left third, with a b/w gradient approximately 1/3 from the left side of the frame, to create the feathering. Than, the remaining 2/3 of the image would be solid black (no pass-through).
You would flip all of these instructions to set up the composite for the right side, as well.

Here’s an example of how to set up Track Mattes in Premiere. It doesn’t show you exactly what you would need to do for your purpose, but it will show you the mechanics of how to use the Track Matte.

https://www.handcranked.newinelabs.com/tutorials/Premiere_Alpha_Channel_Matte.htm

Vince